One of the key pre-checks before vCenter upgrade we often miss out is the Virtual Distributed Switch (vDS) version. One of my customer was planning to upgrade their VCSA from 6.7 to 7.0. In their current infra, they still have mixed of ESXi 6.5 and 6.7 hosts. They also have couple of ESXi 6.0 hosts, used for testing and development, ready to be sunset. These ESXi 6.0 are still connected to the existing Distributed Switch. The vDS was setup with version 6.0.
Part of the upgrade planning, they have gone through all the requirements and all the boxes are checked. Change window was set, vCenter 7.0 ISO was mounted and the installer was executed. At Stage 1, all information were entered and progress bar was moving.
To their dismay, an error was pop-up showing the following:
Upon further checking, we found out that the vCenter was deployed onto a host connected to the vDS with version 6.0. Based on KB52826, the vDS must be at least 6.5 (n-2) before the upgrade can proceed. To upgrade vDS version, you can follow this link.
For now my customer will have to remove out ESXi 6.0 host from the vDS, reconfigure with Standard Switch and upgrade the vDS to version 6.5. Only then they will meet the vDS requirements and proceed with the upgrade. Hope this post help you to add extra checks on vDS setting before upgrading. As a reminder, do keep all vSphere components such as vCenter, ESXi, vDS, VMware Tools and VM Hardware version including Guest OS to the latest version.